The non-binary code (NBC) or the lattice code (LC) has been the only possible channel code with the pulse amplitude modulation (PAM) signaling of modulation size greater than two for the physical layer network coding (PNC) over a decode-andforward (DF) relaying channel. A major drawback with the NBC or LC however is its high computational complexity. In this letter, we present new modified high-order PAMs that enable us to use the computationally efficient b